The invention relates to a method for correcting a fuel injection amount in a common-rail-type fuel injection control device and a common-rail-type fuel injection control device, and more particularly to a method and a device which can realize the enhancement of correction accuracy or the like.
With respect to a fuel injection control for an internal combustion engine, various fuel injection amount correction techniques have been conventionally proposed for correcting the deviation between an actual fuel injection amount and a target fuel injection amount caused by irregularities of characteristics of a fuel injection valve, the deterioration of the fuel injection valve or the like.
For example, in a pilot injection control performed by a fuel injection control device which is configured to perform learning processing of a fuel injection amount, there has been proposed a technique where an amount of variation in an engine speed when injection for learning is performed and an amount of variation in an engine speed when injection for learning is not performed are detected, and a fuel injection amount which is expected to be actually injected (actual fuel injection amount) by a fuel injection valve is calculated based on detected amounts of variation in the engine speed, and the correction of fuel injection amount is performed using the difference between the actual fuel injection amount and a command fuel injection amount as a correction amount thus making the actual fuel injection amount agree with the command fuel injection amount (see JP-A-2005-36788).
To directly measure the actual fuel injection amount is difficult in actual measurement and hence, the technique which calculates the actual fuel injection amount based on a variation amount in an engine speed as described above is a method which is conventionally used since the method can relatively easily acquire the actual fuel injection amount.
As such a technique for acquiring a variation amount in an engine speed, for example, there has been known a technique where the injection of a minute injection amount is performed several times when a vehicle is in a so-called overrun state (non-injection state), and a variation in an engine speed in such a state is detected as a variation in a frequency component of an engine speed, and an actual injection amount is estimated based on the variation in a frequency component, and the correction of the fuel injection amount based on the technique is also performed.
With respect to a vehicle which uses an internal combustion engine represented by a diesel engine, there has been known a vehicle which includes an exhaust brake device which uses an exhaust gas. In such a vehicle, a cylinder internal pressure of an engine when fuel is not injected differs depending on the use or the non-use of the exhaust brake. The difference in such a cylinder internal pressure is small at a relatively low land. However, at a high land, in a case where the injection of minute injection amount is performed several times when the fuel is not injected as described above, a variation in an engine speed which occurs in such a state is detected as a variation in a frequency component of the engine speed, and the correction of fuel injection amount is performed by estimating an actual injection amount based on a variation in a frequency component, there arises a drawback that the difference in the cylinder internal pressure becomes so large that the correction error is induced whereby the difference in the cylinder internal pressure cannot be overlooked.